The healing of damaged or diseased tissues or organs is, in general, imperfect, resulting in scarring and loss of function. The ineffectiveness of pharmacological therapy has led physicians to resort to reconstructive surgery that repairs or reconstitutes soft tissue or skin by introducing an injectable or implantable material. For example, silicon gel, polyester fiber, and polytetrafluorethylene (PTFE) have been extensively used as implants designed to replace diseased or damaged body parts. Other products that have been injected into the human body to correct soft tissue and skin defects include paraffin, petrolatum, vegetable oils, lanolin, and bees wax. Implantation or injection of these synthetic materials, however, can become nazardous to the health of the patient due to leakage, calcium deposit, hematoma, nodules, cellulitis, skin ulcers, and the triggering of autoimmune diseases (e.g., joint swelling and flu-like symptoms).
To reduce immune response caused by the injection or implantation of non-biocompatible materials, hyaluronic acid gel, a non-animal biomaterial, has been used for soft tissue augmentation (Lupton J. and Alster T., 2000, Dermatol. Surg. 26:135-7). Bovine collagen has also gained widespread use as an injectable material for soft tissue augmentation. Collagen is the principal extracellular matrix structural protein. Early collagen implants are often solid collagen masses which were cross-linked with chemical agents, radiation or other means to improve mechanical properties, decrease immunogenicity and/or increase resistance to resorption (see, e.g., Oliver R. et al., 1976, Clin. Orthop. 115:291-30; 1980, Br. J. Exp. Path. 61:544-549; 1981, Conn. Tissue Res. 9:59-62). The main problems associated with solid implants, however, are that they must be implanted surgically and often lose flexibility due to continuing cross-linking in situ. In contrast, while injectable collagen implant materials might have improved volume consistency and resistance to physical deformation, they are expensive and time consuming to prepare.
Also, engineered tissue has been used to augment existing tissue. Tissue engineering is an emerging field that studies the repair or regeneration of damaged or diseased tissues or failing or aging body parts with laboratory-grown parts such as bone, cartilage, blood vessels, and skin. Tissue engineering is based upon a relatively simple concept. First, some building material (e.g., extracellular matrix or biodegradable polymer) is shaped as needed (e.g., scaffold), seeded with living cells (e.g., stem cells), and bathed with growth factors. While the cells multiply, they fill up the scaffold and grow into a three-dimensional tissue. Once implanted in the body, the tissue will function as a substitute for the damaged tissue. As blood vessels attach themselves to the new tissue, the scaffold dissolves, and the newly grown tissue eventually blends in with its surroundings.
In response to the need for more efficient and effective implant materials, extracellular matrix (ECM) and other acellular biomaterials have been used as therapeutic scaffolds for cell attachment and proliferation and as templates for tissue repair (Schmidt C. and Baier J., 2000, Biomaterials 21:2215-31). Extracellular matrix is a complex structural entity surrounding and supporting cells. The extracellular matrix is found within mammalian tissues and is made up of three major classes of biomolecules: structural proteins (e.g., collagen and elastin), specialized proteins (e.g., fibrillin, fibronectin, and laminin), and proteoglycans (e.g., glycosaminoglycans). Although the exact mechanisms through which ECM facilitates repair or regeneration are not known, the composition and the organization of the components are considered to be important factors that influence cell attachment, gene expression patterns, and cell differentiation.
Successful implants include extracellular matrix from decellularized skin, blood vessels, and submucosal tissue. Abatangelo et al. in International Publication No. WO 97/18842 describes the preparation of skin substitutes in vitro by seeding keratinocytes with extracellular matrix secreted by bone marrow stem cells partially or completely differentiated into a specific connective tissue. Naughton in U.S. Pat. No. 5,830,708 describes methods for soft tissue augmentation by injecting extracellular matrix proteins secreted from fibroblasts which were grown on a three-dimensional framework. Bell in U.S. Pat. No. 5,800,537 describes a method for producing tissues for grafting using fragmented extracellular matrix particulates.
Bone marrow ECM is a part of the microenvironment that supports hematopoietic development in the bone marrow. Bone marrow ECM consists of accessory cells, cytokines, and extracellular matrix. The extracellular matrix in the bone marrow is comprised mainly of fibronectin, hemonectin, thrombospondin, collagen, laminin and glycosaminoglycans, heparan sulfate, dermantan, chondrotin sulfate (CS), and hyaluronic acid (HA). Recent findings show bone marrow is a source of multipotent adult stem cells (Jiang et al., 2002, Exp. Hematol. 30:826-904). The ability to interact positively with stem cells is especially important for improving the healing of tissues, such as but not limited to epithelium tissues, connective tissues, muscle tissues, and nerve tissues.
Restenosis is a closure, re-narrowing or blockage of a peripheral or coronary artery at the same site caused by an effort to open an occluded portion of the artery by angioplasty (a balloon procedure to open an obstruction or narrowing of a blood vessel) or stent (an expandable, slotted metal tube, inserted into a vessel) procedure. Restenosis occurs in 40-50% of patients have angioplasty and in 20-30% with the use of stents (Ino T. et al., 1997, Acta. Paediatr. 86:367-71). Restenosis has previously been addressed by providing stents which are seeded with endothelial cells that had undergone retrovirus-mediated gene transfer for either bacterial beta-galactosidase or human tissue-type plasminogen activator (Dichek D. et al. in 1989, Circulation 80:1347-53) or stents coated with antiplatelet agents, anticoagulant agents, antimicrobial agents, antimetabolic agents (U.S. Pat. No. 5,102,417; International Publication No. WO 90/13332). Given the ability of bone marrow ECM to improve healing of tissue, the use of bone marrow ECM as a therapy is likely to improve patient outcome for occluded arteries.
The present inventors have surprisingly found that bone marrow ECM can be isolated, is a rich source of matrix proteins and growth factors, and that injecting or implanting bone marrow extracellular matrix guides tissue repair and regeneration in injured tissue. It is therefore an object of the present invention to provide a pharmaceutical composition, a medical device, as well as a tissue regeneration scaffold comprising a therapeutically significant amount of decellularized bone marrow extracellular matrix.